Chief, and the Spanish for the same, Jefe, both come from the same root: the French chef, which means the same.
But this is odd as they sound so different! How are they related?
It’s not obvious, but it’s easy once you understand the pattern: The Latin sound “sh” and very similar sounds (such as the “ch” and “sy”) almost always became a “j” in Spanish. Like syrup and jarabe. Not obvious!
The Spanish caja (“box”) comes from the Latin capsa for the same.
This gives us a surprising connection to some English words that, on the surface, sound very different than caja:
The Latin turned into the Spanish through an interesting pattern: the ‑sh- sound in Latin consistently turned into the ‑j- sound in Spanish (at first retaining the original pronunciation, but then under the influence of Arabic, grew to the throat-clearing sound). With caja, we have a slight variation of the pattern, where the ‑ps- sound turned into the ‑j- sound. Thus, the c‑ps maps exactly to c‑j.
The Spanish flojo means “slack, loose” — but it is a very common word in Spanish, often used to mean “relaxed” in a negative way, in senses like, “They cut themselves some slack.”
Flojo comes from the Latin fluxus, meaning the same as the Spanish. From fluxus, we get a bunch of English words, including: fluent, fluid, fluctuate and even (via fluent) affluent and influence. We also get the more fun flush and the most obvious flux (as in, “to be in flux.”) All of these can be understood in the sense that, that which is loose flows — and all of these words flow in one way or another: liquids are fluid, you speak fluently, flushing water flows, money flows if you are affluent, etc.
The ‑x- in the original Latin tended to disappear into the English (hence leaving the vowels before and after, as in fluent or fluid) or became a ‑sh- sound. This is an example of the common pattern of the ‑sh- sounds mapping to the throat-clearing ‑j- in Spanish, with the fl-sh of flush mapping to the fl‑j of flojo.
Quejar, Spanish for “to complain” doesn’t seem related to any English equivalent.
But upon closer look, it is a first cousin of both quash and squash.
All come from the Latin quassare, meaning, “to shatter.”
The relationship is easy to see if we remember that the Spanish ‑j- sound used to be the Latin ‑s- sound (and many variants, like ‑ss‑, ‑si‑, ‑sy‑, ‑sh‑, ‑ch‑, etc).
Thus, the qu‑j for quejar maps to the qu-sh of quash and the sq-sh of squash.
Complaining, it seems, is a form of quashing (squashing?) your opponent!
Perejil and its English version parsley sound very different. But they are, actually, etymologically the same word.
They sound different because often the ‑s- and ‑sh- sounds in Spanish turned into the letter ‑j- with the Arabic throat clearing sound as a pronunciation. Thus, the p‑r-j‑l of perejil maps exactly to the p‑r-s‑l of parsley.